Splendid but Unhappy

[littlemanpoet]

I was reading Homesick for Middle Earth one of the many reviews of the new Turin book, and my mind literally stumbled when I read this.

Tolkien's silence says that Middle Earth is a splendid but unhappy world because it has no real god. That is certainly implicit in TLOTR, especially in the postwar sadness of Frodo. Not until he leaves Middle Earth for the home of the gods in the West does he find some hope of happiness. His companion Sam sees him off, and then returns to the Shire and the simple consolations of domestic life.

I'll grant Crawford Kilian the unhappiness point for the nonce, but it is the bolded statement with which I take exception. Lack of gods is what makes Middle Earth both splendid and unhappy? Supposing it was even accurate, how does that work?